Conventionally, sound absorbing bodies have been used to adjust the reverberation within rooms such as for home audio and car audio, and the reverberation within speaker enclosures.
There are basically two methods by which sound absorbing bodies absorb sound, a method that uses the viscous resistance of air and a method that uses attenuation within a material.
As one sound absorbing method that uses the viscous resistance of air, there is a method that uses a porous material, such as soft polyurethane foam, where sound is absorbed within the minute airspace through a portion of the vibrational energy being converted into thermal energy, when a sound wave enters into the porous material, due to the viscous resistance of the air, and due to friction with the surrounding.
As a method that uses the other, that is, internal attenuation, there is a method that uses a membrane or a plate, where sound is absorbed through attenuation within the material through the acoustic energy causing the membrane or plate to vibrate.
However, in these sound absorbing methods, the absorption is not necessarily uniform for sound waves across the audible frequency band, where the porous material is superior in terms of the sound absorption characteristics in the high-frequency range and vibrating the membrane or plate exhibits a peak in the sound absorption characteristics at the resonant frequency thereof.
Moreover, with the porous material it is known that the sound absorption characteristics in the low-frequency band can be improved through a method of increasing the thickness, where effective sound absorption characteristics are present if the thickness is at least ¼ the wavelength of the sound wave, but at a frequency of 100 Hz the thickness would be about 85 cm, and thus the locations wherein sound absorbing bodies with such thicknesses can be installed are inherently limited.
In order to solve such conventional problems, an overall improvement in the sound absorption characteristics has been achieved in the middle and low frequency band with a practical thickness through the formation of a film on the porous material in, for example, Japanese Unexamined Patent Application Publication 2007-34254.
However, the conventional sound absorbing body does not take into consideration acoustic reverberation in uses such as home audio and car audio, and usually sound absorption characteristics that are biased towards the high-frequency band or the low-frequency band, or towards a specific frequency, are seen.
When these sound absorbing bodies, for example, a sound absorbing body having sound absorption characteristics that are biased towards the high-frequency band, are used, the result will be the audio sounding muddy, and when a sound absorbing body having characteristics that are biased towards the low-frequency band are used, the result will be that the sound lacks richness, and sounds barren.
While various combinations of these methods are used in order to solve these problems, determining the optimal combination and installation location requires a high level of knowledge and installation skill, and thus there has been no choice but to rely on an expert in acoustical design.
Moreover, when used in combination, the respective sound absorbing bodies have been arrayed together for use, but in some cases there have been problems with variability in the acoustics depending on the listening point, and cases wherein installation has not been possible due to space problems.
Moreover, for household use there is the need for extreme thinness, given the space problem, for ease in cutting and processing from the perspective of these in installation, simplicity in disposal after cutting, ease in mounting to wall surfaces, and the like, and further, when installed in a location that is likely to be seen, such as within a room, there is also the need for decoration.
The present invention is the result of focus on the conventional problem areas set forth above, and the object of the present invention is to provide a sound absorbing, body that has sound absorbing characteristics that are desirable for the intended use, that is, in suppressing reverberation, within a room, of the sound waves outputted from a speaker or suppressing reverberation within a speaker enclosure, and in maintaining a high sound absorption rate in the mid-frequency band, with flat characteristics, and, in order to be used with ease in a typical home, has a simple structure, can be installed easily, and can be decorated.